Field of the Invention
The invention relates to a voltage-resistant switch and a circuit with said voltage-resistant switch.
Brief Description of the Related Art
Due to the progressing miniaturization of the structures of the components and the associated smaller oxide thicknesses of the gate connectors, there arises the problem in MOS components that the supply voltage Vdd for modern circuits has to be further reduced constantly. In such circuits excessively high supply voltages can lead to damage to or even destruction of the MOS components due to the change of the electric properties.
The voltage-resistance with respect to the drain-source contacts along the channel in so-called high-voltage MOS transistors is achieved substantially through weakly doped drift areas. In order not to impair the electric properties of the MOS transistors, the oxide thickness cannot be increased by any desired degree in order to improve the voltage-resistance. To be able to switch through a voltage signal with a MOS transistor with as little influence as possible, while taking account of the threshold voltage of the MOS transistor, for example in the case of an NMOS transistor, the value of the gate potential must be higher than the drain or the source potential.
In some circuits, however, it is frequently required to switch voltages which are higher than the technologically maximally admissible gate-source voltage. The maximally admissible gate-source voltage can be exceeded therein, which can lead to a damage to or even destruction of the MOS transistor. Such an example is a programmable EEPROM circuit with a signal input in which the maximum value of the input signal at the signal input amounts to 5V during regular operation, but in the programming/erasing mode can amount to a value of +12V/−12V. The individual components of the circuit are dimensioned such that these components can withstand a maximum value of 5V and thus have to be protected against an input signal with a voltage of >5.5V.
From the German published patent application no. DE 1 03 58 048 A1 (Biotronik) a voltage-resistant switch is known, having a switch control unit with a control input and a safety output connected with a switch input of a safety switch. This safety switch is arranged and configured such that the safety switch electrically connects the gate connector of a first MOS switching transistor with the source connector of the first MOS switching transistor in dependence of a safety signal, when the switch control unit emits the safety signal to the safety input of the safety switch, wherein the switch control unit is configured to generate and emit this safety signal.
The U.S. Pat. No. 7,835,126 (Kyocera) shows a short-circuit protection circuit for an internal current source that can be connected with an external unit. The output is equipped with two MOS transistors which are conductive during regular operation. When a short circuit occurs, the voltage at one of the gates of a MOS transistor is increased and the MOS transistor is switched off, i.e. the MOS transistor is no longer conductive. The internal current source is isolated thereby and a damage is thus largely prevented.